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The golden glow of street lights could soon be replaced by the green fluorescence of tree leaves. Scientists from the Academia Sinica and the National Cheng Kung University in Taipei and Tainan have implanted glowing, sea urchin shaped gold nanoparticles, known as bio light emitting diodes, or bio LEDs, inside the leaves of a plant.

The new nanoparticles could replace the electricity powered street light with biologically powered light that removes CO2 from the atmosphere 24 hours a days.

"In the future, bio-LED could be used to make roadside trees luminescent at night," said Yen-Hsun Su in an interview with Chemistry World. "This will save energy and absorb CO2 as the bio-LED luminescence will cause the chloroplast to conduct photosynthesis."

The gold, sea urchin shaped nanoparticles are the key to turning a material that normal absorbs light into one that emits it.

Chlorophyll, the photosynthetic pigment that gives leaves their characteristic green color, is widely known for its ability to absorb certain wavelengths of light. However, under certain circumstances, such as being exposed to violet light, chlorophyll can also produce a light of its own. When exposed to light with a wavelengths of about 400 nanometers the normally green colored chlorophyll glows red.

Violet light is hard to come by though, especially at night, when glowing leaves would be useful to drivers and pedestrians. The scientists needed a source of violet light, and found it in the gold nanoparticles.

When shorter wavelengths of light, invisible to the human eye, hit the gold nanoparticles, they get excited and start to glow violet. That violet light strikes the nearby chlorophyll molecules, excites them, and the chlorophyll then produces the red light.

The scientists, who published their work on bio LEDs in the journal Nanoscale, hope that that trees treated with the gold nanoparticles would produce enough light that they could replace electric or gas street lights.

For now however, the effect is limited to the scientist's test subject, an aquatic plant known as Bacopa caroliniana. Expanding to terrestrial plants, the kind that line streets, should be possible, said Krishanu Ray, a scientist at the University of Maryland, with some additional work.

"They certainly could be used as street lights," said Ray. "But that's a long way away."